Apparatus for wet abrasive blasting



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ATTENEY Sept. 26., L1967 A. H.l EPPLER' l y APPARATUS FOR WET ABRAsIvE BLASTING Filedv March 12, 1965 f Sept. 26, 1967 A H. EPPLER APPARATUS FOR WET' ABRASIVE BLASTING 2 Sheets-Sheet 2 'Filed Marchv 12, 1965 ATTQENEYS United States Patent O 3,343,304 APPARATUS FOR WET ABRASIVE BLASTING Arthur H. Eppler, 2518 W. Wisconsin Ave., Milwaukee, Wis. 53203 Filed Mar. 12, 1965, Ser. No. 439,198

12 Claims. (Cl. 51-8) ABSTRACT OF THE DISCLOSURE This invention relates to an apparatus for wet abrasive blasting.

A slurry of abrasive and liquid Vcarrier s extremely destructive of pumps and other parts of the apparatus which may be exposed thereto. Accordingly, it has become customary to elevate the slurry to the blasting nozzle under relatively low pressure and to use an aspirating jet of air at the nozzle to accelerate the slurry for blasting the work. The slurry being very heavy, the degree of acceleration produced by air under any practicable pressure is inadequate. It is impracticable to supply the slurry to the nozzle under any substantial pump pressure because the pumps used for this purpose will lbe destroyed after a very brief peri-od of usage.

Accordingly, the present invention contemplates the withdrawal of slurry from a sump in the treatment chamber and the storage thereof in a pressure vessel wherein a batch of slurry accumulated at low pressure is subjected to a head of air pressure and is circulated rapidly under circumstances which assure that the abrasive will be maintained in suspension. Since the operation is a batch operation in which the entire vessel is under pressure, the circulation does not involve'any great head resistance. It can, therefore, be laccomplished by a screw rather than a centrifugal or a positive pump.

One particular means for maintaining the abrasive in suspension has proved superior to any other. The screw withdraws'the slurry from the bottom of the batch tank and discharges it at an elevated position therein. From the point of discharge from the screw, the slurry ows by gravity back toward the bottom of the vessel. Enroute,

the slurry is required to pass through small openings in a conical baffle above which a mass of slurry is maintained without great ebullition while below it there is a partial void produced by the withdrawal of slurry by means of the screw at a rate faster than the slurry can ow through the apertures in the conical baiile. This results in great agitation and, apparently, breaks up any tendency of the abrasive particles to agglomerate.

Authorities consulted with regard to the superior results achieved have theorized that there may be a certain amount of ionization of the particles resulting from their passage through the baffles, this being possibly attributable in part to the alkalinity of the carrier liquid, and the lionization tending to keep the particles separate from each other to prevent agglomeration. They further theorize that agglomerated particles have a lbuilt-in cushioning effect which minimizes the abrasive action on the work in relation to the total weight of abrasive used. In contrast, the total abrasive action of individual particles propelled against the work at like speeds will be much greater.

In any event, exhaustive tests have shown thatV the 3,343,304 Patented Sept. 26, 1967 abrasive action on the work is superior when the particles are circulated through the bale and projected under head of air pressure to the nozzle, where a jet of air under slightly higher pressure completes by aspiration the desired acceleration of the particles projected against the work. Using similar apparatus under a similar head of pressure and similar nozzles, but without the particular baile, produces markedly less successful abrasive action.

Because the slurry is pressurized and circulated ina batch, a preferred embodiment of the invention includes a plurality of batch vessels in which the slur-ry is pressurized, the arrangement being such that a vessel from which slurry has been used can Ibe relieved of pressure and refilled while the adjoining vessel is in service. Electrical programming means is used in the preferred embodiment ofv the invention to correlate the treatment of the work with the filling, and pressurizing, and relief of pressure, of the respective vessels.

In the drawings:

FIG. 1 is a diagrammatic view partially in side elevation but largely in section through treating apparatus and one of the batch storage and pressurizing vessels.

FIG. 2 is a detail view taken in section on the line 2- 2 of FIG. l.

FIG. 3 is a fragmentary view on a somewhat reduced scale showing a more highly developed system in which two vessels are used interchangeably, the treatinglchamber being fragmentarily illustrated in an embodiment differing from thatof FIG. l.

FIG. 4 is a fragmentary view in horizontal section through the treating chamber, diagrammatically illustrating in plan the work support and treatment nozzles.

Referring to FIG. 1: The treatment chamber 6 is generally conventional, having work supporting bars at 8 upon which the workpiece 10 is mounted for wet abrasive blast treatment.

Beneath the work is a sump 16 in which the used slurry may accumulate as indicated at 18. A centrifugal pump 20 driven by motor 22 has an inlet 24 provided with screen 26 through which slurry maybe withdrawn from the sump 16 and recirculated through the discharge pipe 28 and returned to the sump, the purpose of this circulation being to maintain in suspension the abrasive content of the slurry 18. Y

In the past, the branch discharge pipe 30` leading from the pump 20 would have extended directly to the slurry inlet 32 of nozzle 14 where it would be subjected to the aspirating effect of air supplied through the line 34 for blasting the workpiece 10. According to the present invention the branch pipe 30 does not lead directly to the nozzle but leads, subject t-o the control of valve 36, into the pressure vessel 38 where batches of slurry can be accumulated from pump 20 under low pressure. A pressure venting line 40 controlled by valve 42 leads from the vessel 38 back to the lower portion of the treatment chamber 6. When it is desired to iill the vessel 38, the interior is reduced substantially to atmospheric pressure by venting air through the line 40.

The pressure vessel 38 has something the shape of anY inverted bottle, its lower wall 44 being conically tapered downw-ardly to a bottom 46 which is immediately beneath the circulating screw 48. A pipe 50 controlled by valve 52 may be used to drain the vessel 38 but, as illustrated, it is equipped with a pressure gauge 54.

The screw 48 is provided with a shaft 56 supported in bearings 58 and 60 at its upper end. The bearings are mounted in a housing 62 supported on the plates 64, 66 which rest on the upper end of the vessel 38. The plates 64 and 66 are both apertured, the latter having the smaller aperture toprovide a shoulder at 68 upon which the flanged sealchamber 70 is mounted. This chamber has upper and lower annular seals 72, 74 which may convenently be made of rubber or the like to embrace the shaft 56. The purpose of the seals is to exclude the abrasive material from the bearings 60 and 58 for shaft 56.

The interior of the chamber 70 contains clear water allowed to circulate by gravity between such chamber and the storage and heat radiating reservoir 76 with which the seal chamber 70 is connected by upper and lower pipes 78 and 80. A water supply line 82 controlled by valve 84 allows make up water to be added as needed. It also maintains the seal chamber under pressure which is at least substantially equal to the pressure in the vessel 38 so that there will be little or no tendency for the abrasive liquid to enter the seal chamber. On the contrary, the tendency is for the water to leak through the seals outwardly of the seal chamber.

The water in the storage reservoir 76 and the seal chamber may not only be subjected to the pressure of water from line 82 but is preferably subjected to air pressure through pipe 85. The pipe 85 connects to the air line 86 which, in practice, has been maintained at 90 lbs. pressure, it being understood that the figure is given by way of example and not by way of limitation. This is the same air line which, subject to the control of valve 88, supplies air through the pressure line 34 to the treating nozzle 14.

The motor 90 is connected by belt 92 with shaft 56 to rotate the screw 48 at high speed. A tubular casing 94 encloses the intermediate part of the screw. The casing is supported on the arms 96 from a sleeve 98 attached to the plate 66 at the top of the vessel 38. The arrangement is such that slurry elevated by the screw is confined within the casing 94 until it is discharged from the screw at the upper end of the casing. See the arrows 100. A rotary slinger 102 on the shaft 56 intercepts any slurry which might otherwise be thrown into the sleeve 92. All such slurry engaged by the slinger 102 on shaft 56 is thrown radially outwardly so that the portion -of shaft 56 above the slinger 102 is substantially free of slurry.

A very important feature of the invention is the pro vision of the conical bale 110 which is mounted on the tubular casing 94 in a position to intercept all slurry elevated in vessel 38 and tending to return by gravity to the bottom of the vessel for recirculation by the screw. The baffle 110 is provided with a very large number of small openings at 112. By way of example and not by way of limitation, it may be stated that the bale performs advantageously if the openings all have the approximate diameter of 3/8 holes on 5X1" centers.

With the vessel 38 lled with slurry to the approximate level from which the vent line 40 opens, the vessel 38 is subjected to air pressure through line 114, manually adjustable reducing valve 116, and shutoff valve 118. Assuming the air supply line 86 to be at 90 lbs. pressure, this pressure also being communicated through reservoir 76 to the seal chamber 70, it has been found expedient to set the reducing valve 116 f-or the delivery of air under 85 lbs. pressure into the upper end of the vessel 38. It will be understood that all figures are given by way of example and not by way of limitation.

With the slurry under the desired pressure in the vessel 38, the motor 90 is started to drive the screw 48 at high speed suiicent to withdraw slurry from below the bale 110 at a rate in excess of the rate at which the slurry will flow through the baffle apertures 112. This will result in a partial void below the baille into which the slurry is constantly being discharged through the apertures 112 with considerable turbulence. Although very turbulent, the mass of slurry immediately above the baie will be relatively non-ebullient. Accordingly, it is from the area immediately above the baffle that slurry under pressure is Withdrawn from vessel 38 through the supply pipe 120, subject to the solenoid valve 122 for delivery to the slurry inlet 32 of the treatment nozzle 14.

All of the slurry used in treatment accumulates in the sump 16 beneath the work 10. None is returned to the vessel 38 until the conclusion of the batch treatment, at which time the vessel is vented through pipe 40. The pump 20 will not be effective to refill the vessel 38. If it has been permitted to continue in operation, the output thereof will have circulated idly back to the sump through the branch line 28. Only after the vessel 38 has been vented is the valve 36 opened so that a major component of the output of pump 20 will then ber delivered into the vessel 38 for a repetition of the batch operation.

The construction shown in FIGS. 3 and 4 is generally similar to that above described but continuous treatment is permitted by an arrangement in which two of the vessels 38 are located side by side as shown in FIG. 3 so that one can be charged while the other is in use.

No claim is made herein to the special treating chamber shown at 7 wherein multiple workpieces 11 are mounted on studs 13, which project radially from the worksupporting turret 15. A shaft 17 supports this turret for clockwise indexing movement in successive increments of each (in the particular embodiment shown).

The chamber 7 is provided with a loading station A defined by partition walls 19 which converge toward shaft 17 and have flexible wiping blades 21 engaged by radial flanges 23 with which the turret 15 is provided. At station A the treated workpieces are removed in each dwell of turret 15 and workpieces to be treated are substituted on the studs 13.

In the first 90 indexing movement of turret 15, the workpiece or workpieces mounted on the stud or studs 13 will be moved to a treating station B in the path of a treatment nozzle nor nozzles 25. A cross head 27 supports these from the ends of reciprocable rods 29 which operate in xed bearings 31 to permit the nozzles 25 to move to and from the work pieces 11 presented thereto. A yoke 33 couples the supporting rods 29 to the ram 35 which is moved in and out of the ram cylinder 37.

It is not necessary to isolate treating station B from treating station C to which the workpieces 11 are advanced in the next 90 indexing movement of turret 15. Here a similar arrangement to that above described permits the ram 39 to move the nozzle or nozzles 41 to and from the work piece or work pieces 11 exposed theret0.

The rinsing station D has its own sump and is isolated from stations C and A by partitions 43 and 19 respectively, each being provided with a wiper blade 21 engaged by one of the anges 23 on the turret. At station D the workpiece or workpieces 11 will be subjected to cleaning blasts from either or both of liquid and air nozzles 45 and 47. At station D all slurry is removed from the workpieces passing therethrough, leaving successive workpieces completed and in readiness for removal and replacement at station A.

From the standpoint of method, it may be maintained that, in the preferred operation of the apparatus shown in FIG. 4, a steady blast is delivered against work pieces 11 at station B while a reciprocating blast is delivered against workpieces at station C by causing the nozzles 41 to reciprocate inwardly and outwardly with respect to the workpieces during treatment. Since the apparatus is not claimed, the details of mechanism for effecting nozzle movement are not shown.

Referring now to FIG. 3, the treatment chamber 7 is here shown in a section which includes a nozzle 25 for projecting slurry against the workpiece 11, the objective being to clean, or remove scale from, or to polish,.the bearing surface 49 in the interior thereof. Nozzle 25 is supplied with slurry under pressure from one or another of the vessels 38 through the pick up lines of the individual vessels, each being provided with its own control valve 122. The slurry received through either valve passes through line 126 to a manifold 128 having as many outlets 130 as may be required to supply t hoses 132 leading to the respective nozzles.

The valves 122 which regulate slurry delivery from the respective vessels 38; the valves 361 which regulate slurry delivery by the pump 20 from the sump 18 to the respective vessels 38; the valves 421 which control the venting of the respective vessels 38; the valves 117 which control the pressurizing of the respective vessels 38 from the air line 86; the valves 89 which control the admission of air to the header 91 which services the several nozzles; are all controlled electrically from a programming device or sequence timer 150 which is also correlated by the electrical connection indicated at 152 with the gear box 154 from which the indexing of turret shaft 17 is operated. The timer function is further regulated from upper and lower limit switches 156, 158 which desirably operate magnetically according to the position of the armature member 160 carried by float 162, the arrangement being duplicated in each of the vessels 38. In short, the programming system (not shown in detail here) is such as to provide complete interlock between the parts to the end that the turret cannot index if any of the vnozzles 25, 41 or 45 is engaged within a workpiece such as that shown at 11. Neither can slurry be discharged from either of the vessels 38 unless that vessel has first been filled and pressurized. Neither can either of the valves 361 open to receive slurry from the sump unless the respective vessel 38 has been vented. It will be understood that instead of showing a complete circuit diagram for effecting the described interlock, the foregoing description is supplemented only by the diagrammatic showing at 166 of electrical Wiring to the respective solenoid valves `from the programming device or sequence timer 150.

In the use of the device pictured in FIGS. 3 and 4, a given vessel 38 will be vented and lled during the indexing of the turret 15. During this indexing movement, the full vessel 38 will be made ready for the use of the slurry therein, the screw 48 being set into motion and the contents of the vessel being pressurized. When, therefore, the indexing movement of the turret 15 has been completed by rotation of its shaft 17, one of the supply valves 122 will be opened to draw from immediately above the -bae 110 of the respective vessel a supply of slurry in which the abrasive is in suspension in a form which minimizes agglomeration of abrasive particles.

It should be noted that in the preferred practice of the invention the slurry contains a chemical additive in solution which changes the pH factor of slurry from 7 to approximately l0. lIt is believed possible that the ionization of the abrasive particles may be at least facilitated by alkalizing the carrier liquid.

The control of the operation by means of the respective floats 162 assures that the blasting operation will be discontinued before one charge is exhausted, thus permitting a new charge to be continuously available for a substantially continuous functioning of the machine notwithstanding that each pneumatic projection of the slurry fromV a given vessel is a batch operation.

In order to disclose fully the best known means of practicing the invention, I herein disclose the following additional particulars. While related to the invention, these are given by way of example rather than by way of limitation, it being understood that I do not wish to limit my claims except as therein stated.

The invention may use any appropriate natural or manufactured metallic abrasive of such character that at least 50 percent of the abrasive used will last for a full 8-hour shift without disintegration into lines. Y

The preferred types of abrasives for the most eicient use of the invention are the manufactured grits consisting of grains or powders of heat-treated aluminum oxide, silicon carbide, boron carbide, tungsten carbide, or oxides of cerium and zirconium. However, natural grits such as diamond, quartz, quartzite, tripoli, garnet, flint, jadeite, nephrite and others may also be used.

With reference to the desirable grain or particle sizes of the abrasives used, when I amusing manufactured aluminum oxide abrasives, the predominant-grain sizes have a broad range between and 800 mesh according to the speed of cutting desired andthe hardness and the shape of the surface to be cut, as well as the diameter of the orice of the blasting gun and the distance at which the gun will be maintained from the work. With regard to natural quartz or other silicates or alumina, the preferred range of predominant grit size is between 60 and 140 mesh. The closer the proximity of the -gun to the work, and the higher the specic gravity of the abrasive, the faster will be the cutting but it may be necessary, according to conventional practice, to make adjustments according to the toughness of the grit in resisting disintegration over a given period of reuse.

The amount of abrasive material to be kept in suspension is widely variable according to conditions. I prefer to use 30 to 50 pounds dry weight of abrasive in t0 50 pounds of aqueous vehicle, assuming that the grit does not exceed average grain size. When larger [grit sizes are used, I prefer to incorporate only 30 pounds dry weight in at least 70 pounds of aqueous vehicle. If the specific gravity of the -grit is reduced, I may, for the same grain size, use as much as 50 pounds of the lighter material with each 50 pounds of the aqueous vehicle.

After the material has been recirculated many times for use over a period of eight to twelve hours of operation, as much as 50 percent of dry Weight of the same abrasive may be added to the slurry to recondition it for continued use. Preferably, however, the slurry is entirely changed and a completely new batch is used after one batch has been in repeated reuse for eight hours.

The preferred air pressure is maintained at about pounds p.s.i. at the source but I have successfully used air pressure all the way from 125 pounds to 1250 pounds p.s.i. If the higher air pressures are used, it is, of course, necessary that the design of the equipment be such that the pressure can safely be handled. Desirably, the air is delivered to the blasting gun orice from an air supply pipe which is engaged within the pipe which furnishes the slurry. However, I have also operated successfully with a gun in which the slurry delivery pipe is .at the center and surrounded bythe compressed air supply line. When multiple guns are supplied with pressure from a single source, the source must be maintained at whatever predetermined minimum is required so that the concurrent operation of a number of guns does not draw down the pressure at the source. The carrier is normally ordinary water. However, I may use any other appropriate liquid carriers such as kerosene, methyl orange, varsol, light petroleum lubricating oils, and other low flash point solvents.

As already stated, it is preferred to use alkalizing agents in the carrier to maintain the pH not lower than 7 and preferably as high as 10. Anyy appropriate proprietary chemical sold for alkalizing purposes can apparently be used. This is a factor which is most appropriatewhen the carrier is ordinary water. v

An alkalizer sold under the trade name Metroluxf has been used successfully at the rate of one-half ounce per gallon of water. This chemical is understood to cornprise trisodium phosphate, sodium chromate and a form of lime which contains boron. Another proprietary chemical sold under the trade name No-Pac is used at the rate of four ounces for each twelve gallons of water. This chemical is understood'to comprise lime which contains boron. In part, this acts as a rust inhibitor and, in part, it functions to maintain the aqueous carrier alkaline. Still another chemical sold under the trade name Cerfacto has been used at the rate of one vounce to each ltwelve gallons of water, where it functions as a non-ionic wetting agent to assist in maintaining the abrasive particles in suspension in the slurry and minimizes agglomeration. IIt is believed that this particular chemical also assists by keepingveach abrasive particle isolated from other abrasive particles and entrained in a single droplet of water. Finally, I have successfully used as an additive a Du Pont product sold under the trade name DuponoL This is employed at the rate of one teaspoonful to twelve gallons of Water.

Referring now to the structure of the mechanism, the preferred thickness or gauge of the material used in the conical baille is ten gauge, this being identical with the outer Walls of the tank and the casing for the screw pump. The taper or angle of the conical baille should be such as to assure the run oif of the abrasives and the minimizing of agglomeration on the baille.

The number and dimensions of the apertures in such conical baille will be related to the interior diameter of the screw pump running through su-ch conical baille and to the r.p.m. of such pump screw and to the inside diameter of such slurry agitating and pressurizing tank Walls to which such conical baille extends from the casing of such screw pump. The apertures should be such as to retard but not prevent the return of the slurry being recirculated to the sump below such screw pump. In the practice which I prefer, the number and dimensions of apertures in the baille have been such that within two minutes after the start of operation of the screw pump, partial vacuum will have been established in the sump area below the baille. In practice, it has been found desirable to have the baille apertures of uniform size. Apertures of diameter on 3A" centers have been used successfully.

An interesting factor concerns the functioning of the baille in reducing or eliminating an electrical static discharge which occurs in the absence of a baille. In experimentation with the device before the baille was added, it was found that an electrical Acharge would accumulate on the slurry vessel notwithstanding conventional grounding precautions in the electrical wiring to the electrically operated parts. After the baille was added and the number and size of apertures adjusted to produce the results described above, it was found that only a mild charge of static would accumulate on the vessel when the pump was started but this was insufficient to discharge or to cause injury and it became dissipated within a minute or two after the pump reached full operation.

Another interesting phenomenon concerns the temperature of the vessel in which the slurry is being recirculated. After the perforated -conical baille plate was incorporated, the temperature of the walls of the vessel below the baille dropped well bel-ow room temperature. It did not drop suiliciently far to frost. However, if the baille is not used there is no observable drop of ternperature in the lower portion of the walls of the slurry vessel.

As for nozzle oriilce sizes and shapes, there is no specific preference as to size but it is preferred that the orifice be round in cross section. All nozzles conventionally employed have been used successfully. In fact, I have used nozzles ranging from the size of a hypoderrnic needle to nozzles having discharge openings -l/s in diameter. If greater effectiveness is desired, it is preferred -to achieve this by increasing the number of nozzles.

The slurry vessel may be of any size and capacity to meet any desired requirements. It may be portable or installed permanently.

The very superior results achieved in the use of the system appear to be dependent, first, upon the pressure with which the slurry is supplied to the nozzle and, secondly, upon the fact that the individual abrasive particles are separate rather than agglomerated, because of recirculation through the baffle. The resulting blast has been used to de-burr harder metals than can be handled with conventional dry or wet blasting. In addition, it has been used to bore holes into and through, as well as to cut into and through, hard metals, ceramics, plastics, stone, cement, and wood and to `do many other works of this type which cannot be done with conventional dry or wet blasting. Also, the apparatus will perform more rapidly and at less expense than operations of which dry or wet blasting are capa-ble.

I claim:

1. For use in wet abrasive blasting, the combination of a storage vessel for slurry used in such blasting, said vessel having upper and lower portion and an intermediate foraminous baille, means for rapidly withdrawing slurry from beneath the baille and delivering it at a point in said vessel above the baille for ilow subject to gravity and pressure differential through the baille, the rate of withdrawal from beneath the baille being in excess of the rate of gravity ilow through the baflle, means for subjecting the interior of the vessel and the slurry therein to pressure materially in excess of atmospheric pressure, and means for discharging slurry under such pressure from a level in said vessel above the baille for use in blasting.

2. A device for supplying slurry of abrasive and carrier liquid to a nozzle to be used in wet abrasive blasting, said device comprising the combination with a hermetically sealed vessel having a foraminous baille subdividing the interior of the vessel into iirst and second portions, a conveyor tube leading from the second portion to the ilrst portion, Ia screw conveyor disposed within the tube and provided with means supporting it for rotation, means for rotating the conveyor at a rate suilicient t-o withdraw slurry from the second portion faster than the slurry can flow by gravity from the iirst portion to the second portion through said baille, means for subjecting the interior of the vessel and the slurry therein to pressure materially in excess 4of atmospheric, and a slurry delivery pipe opening from the ilrst portion of the vessel adjacent the baille and through which slurry which is awaiting passage through the baille can be discharged from the vessel under such pressure.

3. A device according to claim 2 in which the conveyor tube and conveyor screw are upright, the baille being conical and the tube extending through it, the screw having a supporting shaft projecting from the vessel, the means supporting the screw for rotation comprising shaft bearing means disposed above the vessel, the vessel having a seal chamber provided with vertically spaced packing encircling the shaft, and means for supplying liquid to said chamber at a pressure at least equal to that to which the vessel and its contents are subject.

4. A device according to claim 3 in which the means for supplying liquid to the seal chamber includes a closed container having supply and return connections between the container and the seal chamber through which the liquid in the seal chamber may circulate.

5. In a device for wet abrasive blasting using a slurry of abrasive and a liquid carrier therefor, the combination with a blast nozzle having slurry and air inlets, of a batch system for supplying slurry to a slurry inlet of said nozzle, the batch system comprising a hermetically sealed vessel having upper and lower portions and an intervening baille partitioning said vessel and having apertures through which slurry may ilow by gravity and supplemental pressure differential from the upper portion to the lower portion of the vessel, a tube penetrating the baille from the lower portion to the upper portion of the vessel, a screw disposed within the tube and having a supporting shaft extending above the tube and through the top of the vessel, bearing means for the support of said shaft and screw, means for rotating the screw for withdrawal of slurry from the lower portion of the vessel and delivery thereof to the upper portion of the vessel at a rate in excess of that at which the slurry can ilow by gravity through the apertures of the baille, said screw and baille maintaining the abrasive in lsubstantially uniform suspension in the slurry, means for subjecting the interior of the vessel and the slurry contained therein to pneumatic pressure materially in excess of atmospheric, land a discharge pipe opening from the upper portion of said receptacle near the baille and leading to a slurry inlet to said nozzle.

6. A device according to claim in which the bearing means is above the vessel and said vessel is provided with a seal chamber through which said shaft passes, said chamber having upper and lower packing means encircling the shaft, and means for supplying a clear liquid under pressure to the seal chamber for excluding slurry therefrom.

7. A device according to claim 6 in which said last mentioned means includes a closed reservoir for clear liquid, supply and return conduits placing the reservoir in circulatory connection with the chamber, and means for subjecting the reservoir and liquid to pressure in excess of atmospheric and at least substantially as great as the pressure in said vessel.

8. A device according to claim 7 in which a sleeve encircling the shaft depends from the top of the vessel, the shaft being provided with a slinger disposed thereon immediately adjacent the lower end of the sleeve and adapted to intercept nad project radially any slurry which might otherwise pass upwardly into the sleeve toward said chamber.

9. The combination with means for wet abrasive blasting with a slurry of abrasive and carrier liquid and comprising a work support, a sump therebeneath for collecting used slurry, and a blast nozzle having slurry and gas inlets, of means for supplying slurry to the nozzlesluny inlet on a batch basis, said means including a slurry pump having an inlet in the sump and a first outlet branch leading back to the sump, a vessel to which a second outlet branch of said pump leads for pump-induced return to the vessel of slurry previously discharged from the vessel for use, said second outlet branch having a valve for shutting off communication through said second outlet branch between the pump and the vessel, means for subjecting the vessel and slurry therein to pressure materially in excess of atmospheric, a partition dividing the interior of the vessel into upper and lower portions, the partition being provided with apertures for permitting ow of slurry by gravity and supplemental pressure differential from the upper portion to the lower portion of the vessel, a discharge pipe leading from a point near said baffle in the upper portion of the vessel to the slurry inlet of said nozzle for delivery from the vessel for use at said nozzle of slurry subject to the pressure supplied thereto as aforesaid, and means for rapidly circulating slurry within the vessel from the lower portion thereof to the upper portion thereof at a rate in excess of the rate at which the slurry can flow by gravity through the apertures of the baffle, the abrasive content of the slurry being thereby maintained in substantially uniform suspension in the carrier liquid at the point from which pressurized slurry is discharged from the upper portion of the ves,- sel to the nozzle, and means for venting pressure from the vessel as a preliminary to the opening of the valve to accommodate pump-induced flow from the sump back to the vessel.

10. A device according to claim 9 in which the means for circulating slurry from the lower portion to the upper portion of the vessel comprises a conveyor tube disposed in the vessel, the said partition comprising a conical baffle encircling said tube, and a screw conveyor disposed within the tube and having a supporting shaft, bearing means for the shaft, Iand power means connected with the shaft for the rotation of the screw in a direction to elevate slurry from the lower portion to the upper portion of the vessel.

11. A device according to claim 10 in which the tube terminates between the bale and the top of the vessel, means for suspending the tube from the top of the vessel, means in the top of the vessel providing a seal for the shaft, the bearing means for supporting the shaft being above the seal, and means for excluding slurry from the means providing said seal.

12. A device according to claim 10 in which the tube terminates between the upper apex of the baille and the top of the vessel, means for suspending the tube from the top of the vessel, means in the top of the vessel providing a seal for the shaft, the bearing means for supporting the shaft being above the vessel, and means for excluding slurry from said seal, the seal comprising upper and lower packing encircling the shaft, means extending about the shaft from the upper packing to the lower packing and providing a seal chamber, and means for supplying clear liquid to said chamber at a pressure at least as great as that to which the interior of the vessel is subject, whereby any liquid leakage through the packing will be outwardly from said chamber, a sleeve encircling the shaft and depending from the chamber, and slinger means mounted on the shaft adjacent the lower end of the sleeve for intercepting and projecting centrifugally any slurry which might otherwise enter the sleeve in the direction of said packing.

References Cited UNITED STATES PATENTS 2,200,587 5/ 1940 Tirrell 51-8 2,380,738 7/ 1945 Eppler 51--8 2,569,952 10/1951 Ridley 51-12 2,576,008 11/ 1951 Gladfelter et al. 51-8 2,613,482 10/ 1952 Hamacher 51-8 2,667,015 1/1954 Berg 51-12 2,797,530 7/ 1957 Garver 51--8 LESTER M. SWINGLE, Primary Examiner. 

1. FOR USE IN WET ABRASIVE BLASTING, THE COMBINATION OF A STORAGE VESSEL FOR SLURRY USED IN SUCH BLASTING, SAID VESSEL HAVING UPPER AND LOWER PORTION AND AN INTERMEDIATE FORAMINOUS BAFFLE, MEANS FOR RAPIDLY WITHDRAWING SLURRY FROM BENEATH THE BAFFLE AND DELIVERING IT AT A POINT IN SAID VESSEL ABOVE THE BAFFLE FOR FLOW SUBJECT TO GRAVITY AND PRESSURE DIFFERENTIAL THROUGH THE BAFFLE, THE RATE OF WITHDRAWAL FROM BENEATH THE BAFFLE BEING IN EXCESS OF THE RATE OF GRAVITY FLOW THROUGH THE BAFFLE, MEANS FOR SUB- 